Scientists have long been trying to understand how coral reefs support such an amount of fish life despite their location in nutrient-poor waters. According to a new study published on May 23 in the magazine Science, an unlikely group powers these communities: small, mostly bottom-dwelling animals called "cryptobenthic" reef fish.
The study shows that these fish play a key role in coral reefs and supply nearly 60% of the fish food consumed by constantly replenishing their populations in a rapid cycle of life and death.
"Scientists have been arguing over coral reefs for centuries, wondering how such productive, diverse ecosystems will survive in the marine desert," said lead author Simon Brandl, formerly with Smithsonian Tennenbaum Marine Observatories Network and currently a postdoctoral researcher. with Simon Fraser University. "It is noteworthy that these small, almost universally overlooked fish actually serve as the cornerstone of the coral reef fish communities."
Cryptobenthic reef fish, such as gobi, blennies or cardinalfishes, are the smallest of all marine vertebrates. Although they vary in size, the smallest cryptobenthics never reach 1 inch and weigh almost nothing. Other inhabitants of coral reefs eat these fish in large quantities, most during the first few weeks of their existence.
Instead of disappearing, however, the populations of crypto-dinic fish are somehow flourishing in the face of constant predation. Researchers solved this paradox by studying the reef fish larvae. While the larvae of most fish species disperse into the open ocean, where only a few survive, crypto-dentics behaves differently. Brandl and his team found that most cryptobent larvae seem to be close to their parents' cliffs, which is brought to them by many more survivors. These larvae then quickly replace the cryptobent adults eaten on the reef, supporting the growth of larger reef fish.
"We found that larvae of cryptobent fish largely predominate in larvae communities near cliffs that provide a continuous stream of new generations of tiny fish as food for other reef creatures," said Carole Baldwin, co-author of the study and fish curator at the National Museum of Nature. Smithsonian. "It's unbelievable that these fish contribute so much to coral reefs. They're so small that we haven't historically recognized their enormous significance."
Researchers from Australia, Canada, France, and the United States have contributed to this research. The team studied cryptobenthics in Belize, French Polynesia and Australia, combined decades of data on coral reef fish larvae and developed a population model to better understand how cryptobenthics contribute to the diet of coral reef residents.
The study began in 2015, when Brandl was a postdoctoral at the Smithsonian Marine Global Earth Observatory, but these tiny fish are more relevant than ever. As coral reefs go through a dramatic decline, their fish communities – and their dependents – may be at risk. Scientists hope that the vast diversity of cryptobentics and their unique way of life make them a flexible foundation for coral reefs.
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